This invention relates to a printed circuit board (PCB) including a mark which is used as a recognition of an origin for mounting by a mounter. More specifically, this invention relates to a technique which enables proper mounting of devices, on the printed circuit board, including a land which is partially coated with a resist and a land which is not coated with the resist, even if the resist is coated on the printed circuit board at an improper position.
As shown in FIG. 2, a mark 2 made of a conductive leaf or a thin conductor is formed on a prior art printed circuit board 10. When a mounter mounts devices 4, 5 such as electric parts on the printed circuit board 10, the mark 2 is recognized and used as an origin for mounting by the mounter. The mounter is a machine which is used for mounting devices on the printed circuit board. In FIG. 2, a symbol O1 denotes a central point of the mark 2, a symbol 6xe2x80x2 denotes a land on which the device 4 is mounted, a symbol 7 denotes a land on which the device 5 is mounted, and a symbol 8 denotes a resist material (a solder resist). In FIG. 2, there is shown a separation between the outer boundaries of lands 6xe2x80x2 and 7, and the respective boundaries of the surrounding resist 8. In the prior art, the resist 8 is generally coated on the printed circuit board 10 except for the mark 2, the land 6xe2x80x2 and the land 7 respectively.
It will be explained how the mounter mounts the devices 4, 5 on the printed circuit board 10. For the sake of simplicity, only a position in a horizontal direction X, shown in FIG. 2, is considered.
Before mounting the devices 4, 5, the mounter detects the center O1 of the mark 2 from an output of a sensor such as a CCD camera. Then, the mounter mounts the device 4 on a position apart from the center O1 by a distance L1 and also mounts the device 5 on another position apart from the center O1 by a distance L2. These distance values L1 and L2 are previously registered on a data-base provided with the mounter. The value L1 is predetermined, by a design-specification for the printed circuit board 10, as a distance from the center O1 of the mark 2 to a center of the land 6xe2x80x2 and the value L2 is also predetermined, by the design-specification for the printed circuit board 10, as a distance from the center O1 of the mark 2 to a center of the land 7. Therefore, as far as the resist 8 is coated on the printed circuit board 10 except for the the land 6xe2x80x2 and the land 7, the devices 4 and 5 are properly mounted on the land 6xe2x80x2 and the land 7 respectively.
However, as shown FIG. 3(B), in a case that the resist 8 is partially coated onto the land 6, a position error of the device 4 occurs in its mounting for following reasons (1)xcx9c(6). In this case, for the sake of simplicity, only a position in a horizontal direction X, shown in FIG. 3(A) or FIG. 3(B), is considered.
(1) The resist 8 is coated on the printed circuit board 10, which is already provided with the mark 2 and the lands 6, 7, through a mask (not shown) which is put on the board 10. It is assumed that the mask is formed so as to coat the resist 8 on the land 6 except for its central area 6A, and so as to avoid the land 7 by a sufficient clearance and avoid the mark 2 by an extremely sufficient clearance from the resist 8, respectively.
(2) Therefore, if there occurs a few positional errors between the printed circuit board 10 and the mask, a center of the exposed area 6A, which is not coated with the resist 8 out of the land 6, shifts from a center of the land 6 itself.
(3) FIG. 3(A) shows a proper relation between the printed circuit board 10 and the mask. In this case, since the center of the exposed area 6A coincides with the center of the land 6 itself, the center of the exposed area 6A is located at the distance L1 apart from the center O1 of the mark 2, and the device 4 is properly mounted on the exposed area 6A of the land 6.
(4) On the other hand, FIG. 3(B) shows an improper relation between the printed circuit board 10 and the mask. As shown in FIG. 3(B), if the resist 8 is coated with a position error xcex94L1 against the printed circuit board 10, the center of the exposed area 6A is shifted by xcex94L2 from the center of the land 6 itself. Therefor, since the mounter mounts the device 4 at the distance L1 from the center O1 of the mark 2, the device 4 is not properly mounted on the exposed area 6A.
(5) Regarding the land 7, the mask is generally designed so that the minimum gap is assured between the land 7 and the resist 8, even if the mask is shifted a little against the printed circuit board 10. In FIG. 3(B), this minimum gap is illustrated by the left boundaries of the lands 7 being located nearly at the boundary of the resist 8, while the separation between the right boundaries of the lands 7 and the boundary of the resist 8 has increased relative to FIG. 3(A). Therefor, the device 5 is properly mounted on the land 7 in spite of the positional error of the resist 8.
(6) Regarding the mark 2, the mask is generally designed so that a sufficiently wide gap is assured between the mark 2 and the resist 8, even if the mask is largely shifted against the printed circuit board 10. Therefore, the center O1 of the mark 2 is not shifted by the positional error of the resist 8.
An object of the present invention is to provide a printed circuit board and a method, each of which enables proper mounting of devices on the printed circuit board having a land which is partially coated with a resist and a land which is not coated with the resist, even if the resist is shifted against the printed circuit board.
In a preferred embodiment, the present invention is directed to a printed circuit board having a first mark which is formed by a thin conductor or a conductive leaf for mounting a device, a land being partially coated with a resist and a land being not coated with the resist, wherein said printed circuit board further comprises a second mark formed by said resist which is coated on the printed circuit board together with said land being partially coated.
These and other objects of the present application will become more readily apparent from the detailed description given hereafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.